Determinants of mouldy area size in dwellings from the French CONSTANCES population-based cohort

Mould development is a determinant of poor indoor air quality. Data on indoor mould contamination from nationwide population-based studies are scarce. We investigated determinants of mould contamination in the participants from the French CONSTANCES population-based cohort who answered a dedicated follow-up questionnaire in 2019. Participants reported mouldy odour, presence of visible mould and size of mouldy area (spots, <0.2 m2, [0.2 m2-1 m2], ]1 m2-3 m2] or >3 m2) in the bathroom, kitchen, living room and bedroom. Dwelling mouldy area size was defined by the maximum area in one of the four rooms. Logistic models were used to study crosssectional associations between dwelling characteristics and mould contamination adjusted for dwelling type (house/flat), urbanicity and French deprivation index. Stratification by dwelling type, urban/rural areas and least/most deprived neighbourhood were performed. Analyses included 110,470 adults (mean age: 52 years, 54% women, 66% living in houses). Mouldy odour, visible mould and mouldy area size >3 m2 were reported in 2%, 22% and 0.3% of dwellings. Visible mould was more frequently reported in "Ile-de-France" region and in flats than in houses. Heating difficulties, water damage, and occupant-surface ratio were significantly associated with mouldy area size (adjusted(a)OR between 1.58 and 7.30), whereas the presence of a ventilation system and opening the windows in winter were inversely associated (aOR between 0.31 and 0.78). Results did not change by using sum of mouldy area size as an alternative definition. Associations were slightly more evidenced in houses and in the most deprived neighbourhood. Almost one in five participants reported mould contamination in their dwelling. Mouldy area size should be considered for dwelling evaluation to improve the management of mould contamination in France.